Nanoporous matrix and use thereof The invention relates to a nanoporous polyalkoxysilane sol-gel matrix and to a process for producing such a nanoporous polyalkoxysilane sol-gel matrix containing indigo carmine, wherein said process comprises the following steps: • a) synthesizing a gel from tetramethoxysilane or from a mixture of tetramethoxysilane and another organosilicon precursor chosen from phenyltrimethoxysilane, phenyltriethoxysilane, a fluoroalkyltrimethoxysilane, a fluoroalkyltriethoxysilane, a chloroalkylmethoxysilane, a chloroalkylethoxysilane, an aminopropyltriethoxysilane and mixtures thereof, the synthesis being carried out in an aqueous medium in the presence of a polar organic solvent and of the indigo carmine at a temperature ranging from 20 to 70°C, • b) drying the gel obtained in step a) so as to obtain a nanoporous polyalkoxysilane sol-gel matrix containing indigo carmine.